Now that 'Game of Thrones' is ending, here's what you need to know about the new prequel series

Now that 'Game of Thrones' is ending, here's what you need to know about the new prequel series · CNBC

As they say on the fictional Iron Islands of Westeros, "What is dead may never die": Though 'Game of Thrones' is coming to an end on Sunday night, HBO's massively popular fantasy franchise isn't going anywhere.

HBO has at least three spin-off series in the works based on the books of author George R.R. Martin , led off by a prequel series that has reportedly already started filming and could air sometime in 2020. Martin, who has informally been referring to the prequel as "The Long Night," is an executive producer.

While the network has released precious few details about the upcoming prequel, CNBC Make It tracked down some hints from Martin and his writings to glean information about the plot points and characters of the upcoming series. Here's what you need to know.

When does the prequel take place?

According to HBO, and Martin's personal blog , the events of the prequel show will take place near the end of the Age of Heroes, which was anywhere from 5,000 to 10,000 years before the events of the current "Game of Thrones" series ( even Martin says he's not sure of the exact timeline ).

The series will include a period referred to in Martin's books as The Long Night (hence his nickname for the prequel), which in Westeros mythology was when humans first defeated the White Walkers and built The Wall , the massive glacial structure along the northern border of the Seven Kingdoms.

Where does it take place?

Just like "Game of Thrones," the prequel will also take place in the fictional land of Westeros. But because the prequel will be set "thousands of years" before the events of the current series, Martin has warned fans they might not recognize the setting.

"Westeros is a very different place. There's no King's Landing. There's no Iron Throne. There are no Targaryens — Valyria has hardly begun to rise yet with its dragons and the great empire that it built," Martin told Entertainment Weekly in November. "We're dealing with a different and older world and hopefully that will be part of the fun of the series."

What will it cover?

HBO isn't saying much, but the network did release this summary : "Taking place thousands of years before the events of Game of Thrones, the series chronicles the world's descent from the golden Age of Heroes into its darkest hour. From the horrifying secrets of Westeros's history to the true origin of the White Walkers, the mysteries of the East to the Starks of legend, only one thing is for sure: It's not the story we think we know."